Portable, compact smoke generators are widely used for marking a direction and velocity of current air currents or gas flow. They are used to generate a continuous stream of fumes when used with an air supply pump or to produce a small cloud of smoke when used with stroke-type hand pumps.
Conventional smoke generators, commonly called ventilation smoke tubes, operate by passing air over a bed of granular sorbent material impregnated with a substance that reacts with the moisture in the air resulting in dense smoke. One such use of these generators is testing the fitting of respiratory protection equipment, in accordance with OSHA Respiratory Protection Standard 29 CFR 1910.134.
A major drawback of the known art is the use or presence of highly reactive substances that are harmful and must be carefully handled to prevent personal injury or property damage. Typically, the substances are impregnated in carrier materials and sealed glass tubes that include breakable tips. The carrier material is retained in place by mesh-cups and plugs. The process of manufacturing known smoke generators involves many difficult technological steps which result in more costly generators.
Another problem associated with the current smoke generators is the slow reaction between the active reagent and surrounding materials which limits the shelf life of the tubes. Use of glass in the prior art devices presents a hazard to both the user and the generator itself. Edges of broken glass are hazardous when the tube is used in close proximity with humans (such as in the air tight fitting tests for respirators). The use of such glass tubes requires frequent changes of a rubber bulb used widely as a pump because glass particles tend to destroy or limit the life of the pump. The whole construction is bulky and is unsafe.
McConnaughey, U.S. Pat. No. 3,658,719, teaches a smoke generating tube constructed with two reagents that are contained within separate glass ampoules. Each ampoule is enclosed within a perforated envelope of polyethylene tubing. The ampoules have to be broken together to produce smoke. The perforations within each envelope are small in dimension so that transfer of the volatile acid is substantially by diffusion. That is, there is no significant convection flow of gases through the envelope. The above mentioned problems and drawbacks apply to this device. Moreover, it is very difficult to break the glass containers to activate the tube.